All you have to do is use figure A and either multiply or divide by a number to get figure B. In this case, the straight vertical side of Figure A is 6 units, and the straight vertical side of Figure B is 2. So 6 divided by 2 is 3. That means that the scale factor of the triangle is of 3. The triangle contracted it's size by 3.
Refer to the diagram below. Two angles are corresponding to each other when they are on the same line that crosses two parallel lines, one angle is inside the parallel lines, the other is on the outside.